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 Part I. ANA' r O M Y. I77 The coracoid procefs is crooked, with its point incji- The Arm has only one bone, bett known by the Laning forwards ; fo that a hollow is left at the lower fide tin name of ex humeri; which is long, round, and nearof its root, for the paffage of the infra-fcapularis mufcle. ly ftreight. The end of this procefs is marked with three plain The upper end of this bone is formed into a large, furfaces. Into the internal, the ferratus minor anticus round, fmooth head, whofe middle point is not in a is inferred: From the external, one head of the biceps ftreight line with-the axis of the bone, but ftands obliqueflexor cubiti rifes; and from the lower one, the coraco- ly backwards from it.—a—The extent of the head is dibrachialis has its origin. At the upper part of the ftinguilhed by a circular foffa furrounding its bafe, where root of this procefs, immediately before the femilunar the head is united to the bone, and the capfular ligament cavity, a fmooth tubercle appears, where a ligament from of the joint is fixed. Below the fore-part of its bafe the clavicle is fixed. From all the external fide of this two tubercles ftand out: The fmalleft one, which is ficoracoid apophyfe, a broad ligament goes out, which be- tuated moft to the infide, has the tendon of the fubfcacomes narrower where it is fixed to the acromion. pularis mufcle inferted into it. The larger more exFrom the cervix fcapulas the third procefs is produced. ternal protuberance is divided, at its upper part, into The fore-part of this is formed into a glenoid cavity, three fmooth plain furfaces; into the anterior of which, which is of the fhape of the longitudinal fefHon of an the mufculus fupra-fpinatus ; into the middle or largcft, egg, being broad below, and narrow above,.—Between the the infra-fpinatus; into the one behind, the teres mibrims of this hollow, and the fore-part of the root of the nor, is inferted. Between thefe two tubercles, exfpine, a large finuofity is left, for the tranfmiflion of the adUy in the fore part of the bone, a deep long foffa fupra and infra-fpinati mufcles ; and, on the upper part of is formed, for lodging the tendinous head of the bithefe brims, we may remark a fmooth furface, where the ceps flexor cubiti. On each fide of this foffa, as it fecond head of the biceps flexor cubiti has its origin.- defcends in the os humeri, a rough ridge, gently flatThe root of the fiapercilii is rough all round, for the ted in the middle, runs from the roots of the tuberfirmer adhefion.of the capfular ligament of the articu- cles. The tendon of the pedtora! mufcle is fixed into lation, and of the cartilage which is placed on thefe the anterior of thefe ridges, and the latiflimus dorfi, and brims, where it is thick, but becomes very thin as it is teres major, are inferted into the internal one. A litcontinued towards the middle of the cavity, which it tle behind the lower end of this laft, another rough ridge lines all over. may be obferved, where the coraco-brachialis is inferted. The medullary veflels enter the fcapula near the bafe From the back-part of the root of the largeft tuof the fpine. bercle, a ridge alfo is continued, from which the brevis The fcapula and clavicle are joined by plain furfaces, extenfor cubiti rifes.- This bone is flatted on the intipped with cartilage; by which neither bone is allowed fide, about its middle, by the belly of the biceps flexor any confiderable motion, being tightly tied down by the cubiti. In the middle of this plain furface, the en■common capfular ligament, and by a very ftrong one try of the medullary artery is feen flanting obliquely which proceeds from the coracoid procefs; but divides downwards. At the fore-fide of this plane, the bone into two before it is fixed into the clavicle, with fuch a rifes in a fort of ridge, which is rough, and often has a direction, as either can allow this bone to have a fmall great many fmall holes in it, where the tendon of the rotation, in which its pofterior edge turns more back- ftrong deltoid mufcle is inferted; on each fide of which wards, while the anterior one rifes farther forwards ; or the bone is fmooth and flat, where the brachioeus interit can yield to the fore-part of the fcapula moving down- nus rife's. The exterior of thefe two flat furfaces is the wards, while the back-part of it is drawn upwards; in largeft; behind it a fuperficial fpiral channel, formed by both which cafes, thfe oblong fmooth articulated furfaces the mufcular nerve and the veffels that accompany it, of the clavicle and fcapula are not in the fame plane, but runs from behind forwards and downwards.—The body Hand a little tranfverfely, or acrofs each other, and of the os humeri is flatted behind by the extenfors of the thereby.preferve this joint from luxations, to which it fore-arm. Near the lower end of this bone, a large would be fubjedt, if either of the bones was to move on fliarp ridge is extended on its outfidc, from which the the other perpendicularly up and down, without any ro- mufculqs fpinator radii longus, and the longeft head of tation.—The fcapula is connected to the head, os hyoi- the extenfor carpi radialis rife.—Oppofite to this, there des, vertebras, ribs, and arm-bone, by mufcles, that is another final! ridge, to which the aponeurotic tendon, have one end fattened to thefe bones, and the other to that gives origin to the fibres of the internal and external the fcapula, which can move it upwards, downwards, brachioei mufcles, is fixed; and from a little depreifion on backwards, or forwards; by the quick fucceffion of thefe the fore-fide of it, the pronator radii teres rifes. motions, its whole body is carried in a circle. The body of the os humeri becomes gradually broader The ufe of the fcapula is, to ferve as a fulcrum to the towards the lower end, vhere it has feveral proceffes; arm : and, by altering its pofition on different occafions, at the roots of which there is a cavity before, and anoto allow always the head of the os humeri a right fitua- ther behind. The anterior is divided, by a ridge, into ted focket to move in; and thereby to aflift and to en- two; the external, which is the leaft, receives the end large greatly the motions of the fuperior extremity, and of the radius; and the internal receives the coronoid to afford the mufcles which rife from it more advanta- procefs of the ulna in the flefnon of the fore-arm, geous actions, by altering their diredtions to the bone while the pofterior deep triangular cavity lodges the olewhich they are to move, cranon in the extenfions of that member.—The fides of Vol. I. No.'S. Yy the 3